The missing words are: “cloudy white” (often just written as “cloudy” or “milky white”).

Direct answer

In the standard ethanol–water emulsion test for fat, if fat is present, the mixture of ethanol and water becomes cloudy white in colour because tiny fat droplets form an emulsion that scatters light.

Quick explanation (story-style)

Imagine you crush some food, shake it with ethanol to dissolve any fat, then pour this ethanolic solution into water.

If there is fat, it cannot stay dissolved once water is added, so it breaks into microscopic droplets suspended in the liquid.

These droplets act a bit like fog in the air: they scatter light, so instead of staying clear, the tube turns cloudy white / milky.

That’s why exam-style questions expect the sentence to be completed as:

“If fat is present, a mixture of ethanol and water becomes cloudy white in colour.”

TL;DR: The completed sentence is:
“If fat is present, a mixture of ethanol and water becomes cloudy white in colour.”

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